Method for production of porous cross-linked polymer material

ABSTRACT

A method for the production of a porous cross-linked polymer material by the polymerization of an HIPE containing a cross-linking agent, characterized by the fact at least one species of the cross-linking agent is a compound having a double bond equivalent f not less than 120 g/mol. The cross-linking agent is preferred to be a compound possessed of an alkylene oxide moiety or a vinyl polymer containing not less than two polymerizing double bonds in the molecular unit. Thus, it is made possible to produce a porous cross-linked polymer material excellent in absorbency and flexibility, permit the HIPE to be polymerized in a short time, and therefore improve the efficiency of production.

TECHNICAL FIELD

This invention relates to a method for producing a porous cross-linkedpolymer material by polymerizing a water in oil type high internal phaseemulsion (hereinafter referred to as “HIPE”) containing a specificcross-linking agent, and more particularly to a method for producing aporous cross-linked polymer material excellent in absorbancy, mechanicalstrength, and flexibility by incorporating a compound having a doublebond equivalent of not less than 120 g/mol.

BACKGROUND ART

For the production of a porous substance formed of uniform open cellshaving a microscopic diameter, it has been known to obtain a polymer inthe HIPE in the presence of a specific surfactant has been known. The“high internal phase emulsion” as used herein is generally construed asan emulsion containing a dispersion phase at a ratio exceeding 70 vol. %based on the total volume of the emulsion (K. J. Lissant, Journal ofColloid and Interface Science, Vol.22,462(1966)). U.S. Pat. No.5,334,621, for example, discloses a method for producing a porousmaterial by cross-link polymerizing a polymerizing monomer contained insuch an HIPE (hereinafter referred to as “HIPE” method).

This HIPE method produces a porous material by preparing an HIPEcontaining (i) a polymerizing monomer mixture containing an oil-solublevinyl monomer and a cross-linking monomer having not less than twofunctional groups in the molecular unit, (ii) a water phase occupying 90wt. %, preferably 95 wt. %, and particularly preferably 97 wt. %, of theemulsion, (iii) a surfactant such as a sorbitan fatty ester and aglycerol monofatty ester, and (iv) a polymerization initiator andheating the HIPE thereby polymerizing and cross-linking the HIPE.Generally, a porous cross-linked polymer is produced by mixing the oilphase containing at least the components (i) and (iii) mentioned aboveand the water phase of (ii), emulsifying the resultant mixture therebypreparing an HIPE, adding to the HIPE the initiator of (iv) and, at thesame time, heating them to a temperature optimal for polymerizationthereby initiating polymerization. According to this HIPE method, sincethe porous material formed of reticular open cells is produced by thereversed-phase emulsion polymerization, the produced porous material ispossessed of characteristic properties as low density, absorbancy, waterretaining property, heat insulating property, and sound insulatingproperty.

The porous cross-linked polymer material of this quality is a highlybulky substance. For the purpose of producing, transporting, and storingthis bulky material, it is required to possess ample flexibility enoughto resume the original shape after it has been placed in a compressed orbent state for along time. When the porous cross-linked polymer materialis used as an absorbent for humor, it demands excellent absorbancy.

An invention which, with a view to improving the properties ofabsorbancy and flexibility, has originated in the discovery that thisimprovement depends on the distribution of pore diameters in the HIPEhas been disclosed in the official gazette of National Unexamined PatentPublication 10-521,187. This official gazette discloses a method forproducing a porous cross-linked polymer material by using divinylbenzene and 1,6-hexadiol diacrylate as cross-linking monomers,emulsifying them in a specific procedure thereby obtaining an HIPE, andthen polymerizing this HIPE at a temperature of 65° C. for 18 hours.

The production of a macromolecular compound possessed of such areticular texture from the HIPE is accomplished by the formation of athree-dimensionally cross-linked structure. As a technique for obtaininga low density porous cross-linked polymer material possessed of aneffective degree of elasticity, the official gazette of JP-A-62-250,002,for example, discloses a method which is characterized by using aspecific polymerizing monomer and fixing an average pore diameter in aspecific range. This method obtains an elastic cross-linked porouspolymer, for example, by combining up to 50 wt. % of styrene and atleast 50 wt. % of an alkyl acrylate or methacrylate thereby forming anemulsion under controlled treating conditions, and polymerizing themonomer mixture.

The method disclosed in the official gazette of National UnexaminedPatent Publication 10-512,187 as targeted at improving the quality of aporous cross-linked polymer material by controlling the distribution ofpore diameters, however, fails to constitute a method to cure the HIPEin a short time because it requires several hours for polymerization andfails to complete a product in a short time.

When a porous cross-linked polymer material is produced by polymerizingthe HIPE, the mechanical strength of the produced porous cross-linkedpolymer material is varied by difference of the polymerization time.Generally, the polymerization completed in a short time tends to degradethe mechanical strength of the produced porous cross-linking polymermaterial because the formation of a structure of the material isinsufficient. Thus, the produced porous cross-linked polymer materialpossibly sustains a crack due to a break or a bend at the stage offabrication and the stage for storage and transportation. If thepolymerization time is simply elongated, the added time will result in alowering the production efficiency. In this respect, by simplyspecifying the polymerizing monomer to be used as disclosed in theofficial gazette of JP-A-62-250,002, it is still difficult to obtain aporous cross-linked polymer material which secures ample absorbancy andexcels in flexibility.

DISCLOSURE OF THE INVENTION

The present inventors have studied in detail the process for theproduction of a porous cross-linked polymer material by the HIPE methodand have consequently discovered that a porous cross-linked polymermaterial excelling in mechanical strength and in absorbancy as well canbe produced by using a specific compound as a cross-linking agent. Thisinvention has been perfected as a result. Specifically, this inventionis aimed at providing the following item (1).

(1) A method for the production of a porous cross-linked polymermaterial by the polymerization of an HIPE containing a cross-linkingagent, characterized by at least one kind of said cross-linking agentbeing a compound having a double bond equivalent of not less than 120g/mol.

According to this invention, a porous cross-linked polymer materialexcelling in absorbancy and flexibility can be produced by incorporatingin the monomer mixture a compound having a double bond equivalent of notless than 120 g/mol. Moreover, by using the compound having a doublebond equivalent of not less than 120 g/mol, it is made possible toadjust the cross-link density and advance the occurrence of the gelpoint and eventually curtail the polymerizing time. This fact, when theHIPE is continuously polymerized in the form of a sheet, contributes tothe reduction of the space for production because the production timecan be shortened and, at the same time, the apparatus for polymerizationcan be decreased in size. Since the produced porous cross-linked polymermaterial excels in flexibility, it sustains a crack only sparingly whenit is subjected to such additional treatment as the impregnation in achemical agent or when it is folded or bent during storage ortransportation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view illustrating a typical mode ofembodiment of an apparatus for continuous polymerization which is one ofpreferred polymerization devices in the method for production of aporous cross-linked polymer material according to this invention.

101 . . . HIPE, 102 . . . porous cross-linked polymer, 119 . . . HIPEsupplying part, 201 . . . conveyor belt of endless belt type, 202,205 .. . sheet material, 207, 208 . . . unwinding roller, 209,211 . . .roller, 212,213 . . . rewinding roller, 215 . . . polymerizing oven, 217. . . heating means, 219 . . . hot water shower

BEST MODE OF EMBODYING THE INVENTION

This invention concerns a method for the production of a porouscross-linked polymer material by the polymerization of an HIPEcontaining a cross-linking agent, characterized by the fact that atleast one kind of the cross-linking agent is a compound having a doublebond equivalent of not less than 120 g/mol. Since the production of aporous cross-linked polymer material excelling in absorbancy by thepolymerization of an HIPE requires the polymerizing monomer to becross-linked in three-dimension, the HIPE contains a cross-linking agentas an essential component. This invention intends to obtain a porouscross-linked polymer material having the intervals between cross-linksproperly adjusted and excelling in absorbancy and flexibility by usingas the cross-linking agent a compound having a double bond equivalent ofnot less than 120 g/mol. Further, the use of the compound having adouble bond equivalent of not less than 120 g/mol results in adjustingthe intervals between the cross-links, an increase in the density ofcross-links rarely impairs the flexibility of the polymer. As comparedwith the polymerization using a compound having a double bond equivalentof less than 120 g/mol, therefore, the polymerization allowsincorporation in the monomer mixture of the cross-linking agent in alarger amount and use of a cross-linking agent having a larger number ofdouble bonds in the molecular unit. It has been ascertained that theHIPE can be made to succumb more easily to gelation and thepolymerization time can be curtailed as a result. Now, this inventionwill be described in detail below.

[I] Preparation of HIPE

(1) Raw Material Used for HIPE

The raw materials to be used for an HIPE are only required to include(a) a polymerizing monomer, (b) a cross-linking monomer, and (c) asurfactant as essential components for forming an oil phase and (d)water as an essential component for a water phase. They may optionallyinclude further (e) a polymerization initiator, (f) a salt, and (g)other additive as arbitrary components for forming an oil phase and/or awater phase.

(a) Polymerizing Monomer

The monomer composition essential for the composition of the HIPEmentioned above is a polymerizing monomer possessing one polymerizingunsaturated group in the molecule thereof. Though it does not need to beparticularly discriminated but has only to be capable of beingpolymerized in a dispersion or a water-in-oil type high internal phaseemulsion and allowed to form an emulsion consequently. It preferablycontains a (meth)acrylic ester at least partly, more preferably containsnot less than 20 mass % of the (meth)acrylic ester, and particularlypreferably contains not less than 35 mass % of the (meth)acrylic ester.When the (meth)acrylic ester is contained as a polymerizing monomerpossessing one polymerizing unsaturated group in the molecule thereofproves advantageous because the produced porous cross-linked polymerabounds in flexibility and toughness.

As concrete examples of the polymerizable monomer which is usedeffectively in this invention, allylene monomers such as styrene;monoalkylene allylene monomers such as ethyl styrene, α-methyl styrene,vinyl toluene, and vinyl ethyl benzene; (meth)acrylic esters such asmethyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate,isobutyl (meth)acrylate, isodecyl (meth)acrylate, 2-ethylhexyl(meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate,cyclohexyl (meth)acrylate, and benzyl (meth)acrylate;chlorine-containing monomers such as vinyl chloride, vinylidenechloride, and chloromethyl styrene; acrylonitrile compounds such asacrylonitrile and methacrylonitrile; and vinyl acetate, vinylpropionate, N-octadecyl acrylamide, ethylene, propylene, and butene maybe cited. These polymerizable monomers may be used either singly or inthe form of a combination of two or more members.

The content of the polymerizing monomer is preferred to be in the rangeof 10-99.9 mass %, based on the total mass of the monomer compositionconsisting of the polymerizing monomer and a cross-linking monomer. Thereason for this range is that the produced porous cross-lined polymer isenabled to acquire pores of minute diameters. The range is morepreferably 30-99 mass % and particularly preferably 30-70 mass %. If thecontent of the polymerizing monomer is less than 10 mass %, the producedporous cross-linked polymer will be possibly friable and deficient inwater absorption ratio. Conversely, if the content of the polymerizingmonomer exceeds 99.9 mass %, the porous cross-linked polymerconsequently produced will be possibly deficient in strength and elasticrecovery power and incapable of securing sufficient amount of waterabsorbed and sufficient velocity of water absorption.

(b) Cross-linking Agent

This invention is characterized by using as a cross-linking agent acompound having a double bond equivalent of not less than 120 g/mol. Ithas been known, in the production of a porous cross-linked polymermaterial by the polymerization of an HIPE, to use as part of the monomercomponent a cross-linking agent such as divinyl benzene. It has beenalso known that the performance of the porous cross-linked polymermaterial is varied by the cross-linking agent. Under the productionconditions for making the polymerization complete in a short time by theuse of divinyl benzene, however, the porous cross-linked polymermaterial becomes a friable material which is deficient in such physicalproperties as flexibility and compressive strength. This invention iscapable of producing a porous cross-linked polymer material excelling inabsorbancy, compressive strength, and flexibility in a short time byusing a compound having a double bond equivalent of not less than 120g/mol. Properly, the double bond equivalent is in the range of120-10,000 g/mol, preferably 140-5,000 g/mol. If the double bondequivalent falls short of 120 g/mol, the shortage will possibly tightenexcessively the texture near the points of cross-linkage and render theporous cross-linked polymer material rigid and friable.

Generally, in the homopolymerization of a polyfunctional vinyl monomeror the copolymerization thereof with a monovinyl monomer, a prepolymerhaving a linear structure containing a pendant vinyl group or apartially looped'structure resulting from intramolecular cyclization isformed during the initial stage of polymerization. As the polymerizationadvances, the cross-linking reaction between the growth radical and thependant vinyl group in the prepolymer is activated to convert theprepolymer into a macromolecular compound having a highly branchedtexture and compel the polymerization solution to gain in viscosity.This variation of the polymerization system, particularly the growingtrend of viscosity, accelerates abruptly with the approach of a certainpolymerization ratio. Eventually, this polymerization forms a gel whichis a mega-molecule possessed of insoluble three-dimensional reticularstructure and the polymerization solution is deprived of flowability.The polymerization ratio at which the gel begins to form in the systemis referred to as “gel point.” The polymerization reaches the gel pointearlier in proportion as the number of functional groups in thecross-linking agent is heightened and the amount of the cross-linkingagent to be incorporated in the monomer mixture is increased. When thecross-linking agent to be used has a double bond equivalent of less than120 g/mol and has a large number of functional groups or it isincorporated in a large amount in the monomer mixture, the possibilityof the produced polymer being degraded in flexibility increasesfrequently. This invention, because of the use of a compound having adouble bond equivalent of not less than 120 g/mol, allows thecross-linking agent to be incorporated in an increased amount withoutany fear of inducing the degradation of the flexibility, permitsformulation of a composition using a cross-linking agent having anincreased number of functional groups and expediting the occurrence ofthe gel point, and eventually promises a reduction in the polymerizationtime.

The expression “double bond equivalent” as used herein is construed asdenoting the quotient of the division, molecular weight of cross-linkingagent/number of double bonds in the molecular unit.

The cross-linking agent to be used in this invention does not need to beparticularly discriminated but is only required to be a compound havinga double bond equivalent of not less than 120 g/mol. As concreteexamples of the cross-linking agent, i) a compound possessed of not lessthan two double bonds in the side chain or at the terminal andcontaining an alkylene oxide moiety; ii) a vinyl polymer possessed ofnot less than two double bonds in the side chain or at the terminal;iii) a compound obtained by addition polymerizing to an activehydrogen-containing amino group contained in a polyalkylene imide analkylene oxide in an amount exceeding the equivalent of the activehydrogen of the amino group and then binding (meth)acrylic acid by esterlinkage to the resultant polyamine polyalkylene oxide compound; iv) acompound obtained by bonding not less than two molecules of anunsaturated carboxylic acid monomer by ester linkage to an oligo or apolyester possessed of a hydroxyl group; and v) a compound obtained bybonding not less than two molecules of an unsaturated carboxylic acidmonomer by urethane linkage to an oligo or a polyurethane may be cited.These cross-linking agents are invariably possessed of flexibilityinherently and capable of imparting flexibility, compressive strength,and absorbancy to the porous cross-linked polymer material. Among them,the cross-linking agents of i) and ii.) prove particularly advantageousin respect that they excel in the effect of imparting flexibility andabsorbancy to the porous cross-linked polymer material and the effect ofcurtaining the polymerization time of an HIPE. Now, these cross-linkingagents will be described below.

i) As a concrete example of the compound possessed of not less than twodouble bonds in the side chain or at the terminal and containing analkylene oxide moiety, a compound obtained by adding an alkylene oxideto a polyhydric alcohol having a valency of at least two and thenbonding an unsaturated carboxylic acid monomer to the resultant adductby ester linkage may be cited.

The polyhydric alcohols include ethylene glycol, propylene glycol,polyethylene glycol, glycerol, trimethylol ethane, trimethylol propane,bisphenol A, pentaerythritol, and dipentaeryrhritol, for example.

As concrete examples of the alkylene oxide to form an alkylene oxidemoiety for linkage with the polyhydric alcohol, ethylene oxide,propylene oxide, isobutylene oxide, 1-butene oxide, 2-butene oxide,trimethyl ethylene oxide, tetramethylene oxide, tetramethyl ethyleneoxide, butadiene monooxide, octylene oxide, styrene oxide, and1,1-diphenyl ethylene oxide may be cited. For the sake of thisinvention, the alkylene oxide moiety may be a polyalkylene oxideobtained by polymerizing not less than two moles of one or more speciesof the alkylene oxide mentioned above. The alkylene oxide moieties to bebound to one molecule of polyhydric alcohol may be the same ordifferent. The degree of polymerization of alkylene oxide does not needto be particularly restricted so long as the produced compound possessesa double bond equivalent of not less than 120 g/mol.

As concrete examples of the unsaturated carboxylic acid monomer to bebound to the alkylene oxide moiey, such ethylenic carboxylic acids as(meth)acrylic acid, maleic acid, fumaric. acid, maleic anhydride,itaconic acid, citraconic acid, and crotonic acid may be cited.

As particularly preferred cross-linking monomers possessed of analkylene oxide moiety, it is commendable to use an acrylate of propyleneoxide adduct of glycerin answering the following general formula (I)wherein R represents a hydrogen atom and a=b=c=1 is satisfied (made byNippon Kayaku Co., Ltd. And sold under the trademark designation of“Kayarad GPO-303”) and an acrylate of propylene oxide adduct oftrimethylol propane answering the following general formula (II) whereinR′ represents an ethyl group and a =3, b=0, and m=1 are satisfied (madeby Nippon Kayaku Co., Ltd. And sold under the trademark designation of“Kayarad TPA-330”). In the general formula (II), “a” means a number ofbinding site of CH₂O—[CH₂CH(CH₃)O]_(m) COCR═CH₂ unit to a carbonadjoining R′, “b” a number of binding site of CH₂OCOC═CH₂ unit to thecarbon.

(wherein the plurality of R's may be the same or different and are eachhydrogen atom or a methyl group and a, b, and c are each 0 or an integerand satisfy a+b+c≧1.)

(wherein the plurality of R's may be the same or different and are eacha hydrogen atom or a methyl group, R′ represents a methyl group or anethyl group, m, a, and b are each 0 or an integer, and satisfy m≧1 and a+b=3.)

ii) As a vinyl polymer or oligomer possessed of not less than two doublebonds in the side chain or at the terminal, the polymer of anunsaturated carboxylic acid monomer possessed of a plurality ofpolymerizing double bonds in the molecular unit proves advantageous inrespect that the produced porous cross-linked polymer material excels inthe balance between mechanical strength and flexibility.

The vinyl polymer mentioned above is only required to be a vinyl polymerwhich is possessed of a plurality of polymerizing double bonds in themolecular unit. Liquid polybutadiene and (meth)acryl cross-linkingpolymers possessed of a plurality of polymerizing double bonds in themolecular unit may be cited as concrete examples, though notexclusively. (Meth)acryl cross-linking polymers possessed of a pluralityof polymerizing double bonds in the molecular unit prove advantageous inrespect that the produced porous cross-lined polymer material excels inthe balance between mechanical strength and flexibility.

Such a (meth)acryl cross-linking polymer possessed of a plurality ofpolymerizing double bonds in the molecular unit as mentioned above canbe obtained, for example, by a method which comprises first synthesizinga (meth)acryl polymer possessed of a functional group in the molecularunit by. copolymerizing an unsaturated monomer possessed of a functionalgroup during the synthesis of a (meth) acryl polymer and subsequentlycausing this (meth)acryl polymer to react with a polymerizing monomerpossessed of another functional group having reactivity with thefunctional group mentioned above.

As concrete examples of the combination of two functional groups havingreactivity, carboxyl group and glycidyl group, carboxyl group andhydroxyl group, carboxyl group and amino group, carboxyl group andoxazoline group, carboxyl group and aziridine group, hydroxyl group andacid anhydride, and hydroxyl group and isocyanate group may be cited,though not exclusively. The polymerizing monomer possessed of such acombination of functional groups ought to be copolymerized with a(meth)acryl monomer and other polymerizing monomer does not need to beparticularly discriminated. From the viewpoint of the ease and theconvenience of the reaction, however, a method using the reaction of anunsaturated epoxy compound with a (meth)acryl polymer possessed of acarboxyl group and/or a method using the reaction of an unsaturated acidwith a (meth) acryl polymer possessed of a glycidyl group provepreferable.

The weight average molecular weight of the vinyl polymer is preferablyin the range of 2,000-500,000, more preferably in the range of5,000-100,000, and still more preferably in the range of 10,000-40,000.If the weight average molecular weight of the vinyl polymer is less than2,000, the shortage will be at a disadvantage in possibly causing theproduced porous cross-linked polymer material to suffer from deficiencyin flexibility. Conversely, if the weight average molecular weightexceeds 500,000, the excess will be at a disadvantage in possiblyheightening the viscosity of the oil phase and rendering the preparationof an HIPE difficult.

The double bond equivalent of the vinyl. polymer, i.e. the molecularweight of one polymerizing double bond, is preferably in the range of200-10,000 g/mol, more preferably in the range of 500-8,000 g/mol, andmost preferably in the range of 500-5,000 g/mol. The double bondequivalent mentioned above is obtained as “the quotient of the division,molecular weight of vinyl polymer/number of polymerizing double bondscontained in the polymer molecule unit.” If the double bond equivalentof the vinyl polymer mentioned above exceeds 10,000 g/mol, the excesswill be at a disadvantage in possibly causing the produced porouscross-linked polymer material to suffer from deficiency in mechanicalstrength and flexiblity. Conversely, if the double bond equivalent ofthe vinyl polymer mentioned above is less than 200 g/mol, the shortagewill be at a disadvantage in possibly heightening the viscosity of theoil phase and rendering the preparation of an HIPE difficult.

As a vinyl polymer for obtaining a porous cross-linked polymer materialallowing easy preparation of an HIPE without heightening the viscosityof the oil phase and excelling in physical properties, a reacting liquidpolymer which is described in the official gazette of Patent Application2000-54,126 proves preferable. This official gazette discloses a methodfor polymerizing 60-99.9% of an acrylate of an aliphatic alcohol of 4-16carbon atoms in the presence of mercaptan, preferably a method forproducing a polymer possessed of a stellate structure obtained by usinga polyvalent mercaptan as a mercaptan. According to this officialgazette, the polymer of the stellate structure mentioned above producesa reacting polymer which has a weight average molecular weight of notless than 2,000, viscosity at 23° C. of not more than 100,000 cps, and apolymerizing unsaturated group concentration in the range of 500-10,000g/mol and contains at least two polymerizing double bonds in themolecular unit. Since this reacting polymer manifests low viscosity,represses the possible rise of the viscosity of the oil phase when usedas an oil phase component, facilitates manufacture of an HIPE, andabounds in plasticity as a cross-linking agent itself, it allowsproduction of a cross-linking polymer material excelling in plasticityand strength.

Next, iii) the compound obtained by addition polymerizing to an activehydrogen-containing amino group contained in a polyalkylene imide analkylene oxide in an amount exceeding the equivalent of the activehydrogen of the amino group and then binding (meth)acrylic acid by esterlinkage to the resultant polyamine polyalkylene oxide compound will bedescribed below. The polyalkylene polyamine to be used in thecross-linking agent is a compound containing an alkylene group and anamino group. The amino group includes primary amino group, secondaryamino group, and tertiary amino group. Concrete examples of thepolyalkylene polyamine include compounds having such ethylene groups asethylene diamine, diethylene triamine, triethylene tetramine, andtetraethyl pentamine bound thereto with an amino group and polyalkyleneimine. This invention prefers use of polyalkylene imine.

The polyalkylene imine can be obtained by polymerizing such alkyleneimine as ethylene imine, propylene imine, 1,2-butylene imine,2,3-butylene imine, or 1-dimethylethylene imine by the ordinary method.Besides the homopolymers of such alkylene imines, this invention findspolyalkylene imines obtained by mixing two or more species of alkyleneimine, i.e. mixtures of ethylene imine and propylene imine, usable.Among them, polyethylene imine and polypropylene imine proveparticularly preferable. Such a polyalkylene imine is commendablebecause it is cross-linked three-dimensionally in consequence ofpolymerization and is generally caused to contain a primary amino groupand a secondary amino group, i.e. active hydrogen-containing aminogroups, besides a tertiary amino group in the structure thereof.

Then, an alkylene oxide is added to the active hydrogen-containing aminogroup of the polyalkylene polyamine. As the alkylene oxide, the samecompound as cited by way of example in i) above can be used. The numberof addition polymers of alkylene oxide does not need to be particularlyrestricted so long as the produced cross-linking agent has a double bondequivalent weight of not less than 120 g/mol. Generally, the alkyleneoxide, for example, is added to the active hydrogen-containing aminogroup of a polyalkylene polyamine in the presence of a reactioncatalyst. As the reaction catalyst, any of the known catalysts can beused without any particular restriction. Generally, any one of (a) theanionic polymerization using a hydroxide of alkali metal such as sodiumhydroxide, potassium hydroxide, or lithium hydroxide, a strong alkalisuch as alcoholate, or an alkylamine as a basic catalyst, (b) thecationic polymerization using a halogenide, mineral acid, or acetic acidof metal or half metal as a catalyst, and (c) the coordinationpolymerization using a combination of an metal alkoxide of aluminum,iron, or zinc, an alkaline earth compound, and Lewis acid. Subsequently,an unsaturated carboxylic acid monomer is bound to the alkylene oxidemoiety by ester linkage. As the unsaturated carboxylic acid monomer tobe used in this case, the same compound as explained in i) can be used.

iv) As a concrete example of the compound obtained by bonding not lessthan two molecules of an unsaturated carboxylic acid monomer by esterlinkage to an oligo or a polyester possessed of a hydroxyl group orobtained by amide linkaging of an saturated amide monomer, the compoundswhich have an unsaturated carboxylic acid monomer described in i)esterified with a known polyester compound by the known method may becited.

v) Then, as a concrete example of the compound obtained by bonding notless than two molecules of an unsaturated carboxylic acid monomer byurethane linkage to an oligo or a polyurethane, the compounds which havean unsaturated carboxylic acid monomer described in i) bonded to theknown urethane by urethane linkage may be cited.

In this invention, only one species of the compound having a double bondequivalent of not less than 120 g/mol can be used singly or two or morespecies of such compound can be used in combination as the cross-linkingagent.

The amount of the cross-linking monomer having a double bond equivalentof not less than 120 g/mol to be used is preferably in the range of 1-90mass %, more preferably in the range of 10-70 mass %, and particularlypreferably in the range of 20-60 mass %, based on the total mass of themonomer component which comprises the polymerizing monomer mentionedabove and the cross-linking agent. If the amount of the cross-linkingmonomer to be used is less than 1 mass %, the shortage will be possiblyat a disadvantage in causing the produced porous cross-linked polymermaterial to suffer from deficiency in strength and elastic recovery andinsufficient amount of absorption per unit volume or unit weight andfailing to secure absorption of water in a sufficient amount at asufficient speed. Conversely, if the amount of the cross-linking monomerto be used exceeds 90 mass %, the excess will be possibly at adisadvantage in causing the porous cross-linked polymer material tobecome friable and deficient in the water absorption ratio.

Further, this invention may use one species or two or more species ofthe known other cross-linking agent in combination with the compoundhaving a double bond equivalent of not less than 120 g/mol. Thecross-linking agent that can be additionally used is only required to bepossessed of at least two polymerizing unsaturated groups in themolecular unit. It does not need to be particularly discriminated but isonly required, similarly to the polymerizing monomer mentioned above, tobe capable of polymerizing in a disperse or water in oil type highinternal phase emulsion and forming cells.

As concrete examples of the other cross-linking agent, aromatic monomerssuch as divinyl benzene, trivinyl benzene, divinyl toluene, divinylxylene, divinyl naphthalene, divinyl alkyl benzenes, divinylphenanthrene, divinyl biphenyl, divinyl diphenyl methane, divinylbenzyl, and divinyl phenyl ether; oxygen-containing monomers such asdivinyl furane, sulfur-containing monomers such as divinyl sulfide anddivinyl sulfone; aliphatic monomers such as butadiene, isoprene, andpentadiene; and ester compounds of polyhydric alcohols with acrylic acidor methacrylic acid such as ethylene glycol di (meth) acrylate,diethylene glycol di (meth) acrylate, 1,3-butane diol di(meth)acrylate,1,4-butane diol di(meth)acrylate, 1,6-hexane diol di(meth)acrylate,trimethylol propane di(meth)acrylate, trimethylol propanetri(meth)acrylate, pentaerythritol di(meth)acrylate, dipentaerythritoldi(meth)acrylate, dipentaerythritol tetra(meth)acrylate, N,N′-methylenebis(meth)acrylamide, triallyl isocyanurate, triallyl amine,tetraallyloxy ethane, hydroquinone, catechol, resorcinol, and sorbitolmay be cited.

The amount of such “other cross-linking agent” to be incorporated ispreferably in the range of 0-95 mass %, more preferably in the range of0-85 mass %, and particularly preferably in the range of 0-65 mass %,based on the total mass of the cross-linking agent. If the amount of theother cross-linking agent to be incorporated exceeds 95 mass % of thetotal mass of the cross-linking agent, the excess will be at adisadvantage in preventing the compound of a double bond equivalent ofnot less than 120 g/mol from manifesting the effect thereof.

(c) Surfactant

The surfactant which is essential for the composition of the HIPEmentioned above does not need to be particularly discriminated but hasonly to be capable of emulsify a water phase in an oil phase forming theHIPE. It is not limited to the specific examples cited above but may beselected from the nonionic surf actants, cationic surfactants,amphoteric surfactants heretofore known to the art.

Among these surfactants, as concrete examples of the nonionic surfactant, nonyl phenol polyethylene oxide adduct; block polymer ofethylene oxide and propylene oxide; sorbitan fatty acid esters such assorbitan monolaurate, sorbitan monomyristylate, sorbitan monopalmitate,sorbitan monostearate, sorbitan tristearate, sorbitan monooleate,sorbitan trioleate, sorbitan sesquioleate, and sorbitan distearate;glycerin fatty acid esters such as glycerol monostearate, glycerolmonooleate, diglycerol monooleate, and self-emulsifying glycerolmonostearate; polyoxyethylene alkyl ethers such as polyoxyethylenelauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearylether, polyoxyethylene oleyl ether, and polyoxyethylene higher alcoholethers; polyoxyethylene alkylaryl ethers such as polyoxyethylenenonylphenyl ether; polyoxyethylene sorbitan fatty acid esters such aspolyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitanmonomyristylate, polyoxyethylene sorbitan monopalmitate, polyoxyethylenesorbitan monostearate, polyoxyethylene sorbitan tristearate,polyoxyethylene sorbitan monooleate, and polyoxyethylene sorbitantrioleate; polyoxyethylene sorbitol fatty acid esters such as tetraoleicacid polyoxyethylene sorbit; polyoxyethylene fatty acid esters such aspolyethylene glycol monolaurate, polyethylene glycol monostearate,polyethylene glycol distearate, and polyethylene glycol monooleate;polyoxyethylene alkyl amines; hydrogenated polyoxyethylene castor oil;and alkyl alkanol amides may be cited. These nonionic surf actantshaving HLB values of not more than 10, more preferably in the range of2-6, prove preferable. It is permissible to use two or more suchnonionic surfactants in combination. The combined use possibly resultsin stabilizing the HIPE.

As concrete examples of the cationic surfactant, quaternary ammoniumsalts such as stearyl trimethyl ammonium chloride, ditallow dimethylammonium methyl sulfate, cetyl trimethyl ammonium chloride, distearyldimethyl ammonium chloride, and alkylbenzyl dimethyl ammonium chloride;alkyl amine salts such as coconut amine acetate and stearyl amineacetate; alkyl betaines such as lauryl trimethyl ammonium chloride,lauryl betaine, stearyl betaine, and lauryl carboxymethyl hydroxyethylimidazolinium betaine; and amine oxides such as lauryl dimethyl amineoxide may be cited. The use of the cationic surfactant can impartexcellent antibacterial properties to the porous cross-linked polymerwhen the polymer is used for an absorbent material, for example.

The anionic surfactant of a kind possessing an anionic moiety and anoil-soluble moiety can be advantageously used. As concrete examples ofanionic surfactant, such reactive anion emulsifiers possessed of adouble bond as, for example, alkyl sulfates such as sodium dodecylsulfate, potassium dodecyl sulfate, and ammonium alkyl sulfate; sodiumdodecyl polyglycol ether sulfate; sodium sulforicinoate; alkylsulfonates such as sulfonated paraffin salts; sodium dodecyl benzenesulfonate, alkyl sulfonates such as alkali metal sulfates of alkaliphenol hydroxyethylene; higher alkyl naphthalene sulfonates; fatty acidsalts such as naphthalene sulfonic acid formalin condensate, sodiumlaureate, triethanol amine oleate, and triethanol amine apiate;polyoxyalkyl ether sulfuric esters; sulfuric esters of polyoxyethylenecarboxylic ester and polyoxyethylene phenyl ether sulfuric esters;succinic acid dialkyl ester sulfonates; and polyoxy ethylene alkyl arylsulfates may be cited. An HIPE may be prepared by using an anionic surfactant in combination with a cationic surfactant.

The combined use of the nonionic surfactant and the cationic surfactantmay possibly improve the HIPE in stability.

The content of the surfactant mentioned above is properly in the rangeof 1-30 mass parts, preferably 3-15 mass parts, based on 100 mass partsof the total mass of the monomer composition consisting of thepolymerizing monomer and the cross-linked monomer. If the content of thesurfactant is less than 1 mass part, the shortage will possibly depriveof. the HIPE of stability of dispersion and prevent the surfactant frommanifesting the effect inherent therein sufficiently. Conversely, if thecontent of the surfactant exceeds 30 mass parts, the excess willpossibly render the produced porous cross-linked polymer unduly friableand fail to bring a proportionate addition to the effect thereof and doany good economically.

(d) Water

The water essential for the composition of the HIPE mentioned above maybe city water, purified water or deionized water. Alternatively, with aview to utilizing to advantage the waste water resulting from theproduction of the porous cross-linked polymer, this waste water may beadopted in its unmodified form or after undergoing a prescribedtreatment.

The content of the water may be suitable selected, depending on the kindof use (such as, for example, an absorbent material, sound insulationmaterial, or filter) for which the porous cross-linked polymerpossessing continuous cells is intended. Since the hole ratio of theporous cross-linked polymer material is decided by varying the waterphase/oil phase (W/O) ratio of the HIPE, the. amount of water to be usedis automatically decided by selecting the W/O ratio calculated toproduce a hole ratio which conforms to the use and the purpose of theproduced material.

(e) Polymerization initiator

For the purpose of accomplishing the polymerization of an HIPE in a veryshort period of time as aimed at by this invention, it is advantageousto use a polymerization initiator. The polymerization initiator is onlyrequired to be suitable for use in the reversed phase emulsionpolymerization. It is not discriminated between the water-soluble typeand the oil-soluble type.

As concrete examples of the water-soluble polymerization initiator whichis used effectively herein, azo compounds such as2,2′-azobis(2-amidinopropane) dihydrochloride; persulfates such asammonium persulfate, potassium persulfate, and sodium persulfate;peroxides such as potassium peracetate, sodium peracetate, sodiumpercarbonate, potassium peracetate may be cited. As concrete example ofthe oil-soluble polymerization initiator which is used effectivelyherein, peroxide such as, cumene hydroperoxide, t-butyl hydroperoxide,t-butylperoxide-2-ethylhexyanoate di-t-butyl peroxide, diisopropylbenzene hydroperoxide, p-methane hydroperoxide, 1,1,3,3-tetramethylbutylhydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, benzoyl peroxide,and methylethyl ketone peroxide may be cited. These polymerizationinitiators may be used either singly or in the form of a combination oftwo or more members.

Combined use of two or more kinds of polymerization initiator havingdifferent 10 hour half period temperatures, i.e. the temperatures atwhich the concentrations of the relevant initiators are halved in 10hours proves advantageous. As a matter of course, it is permissible touse in combination the water-soluble polymerization initiator and theoil-soluble polymerization initiator.

The content of the polymerization initiator mentioned above is properlyin the range of 0.05.-25 mass parts, preferably 1.0-10 mass parts, basedon 100 mass parts of the total mass of the monomer compositionconsisting of a polymerizing monomer and a cross-linking monomer, thoughit is variable with the combination of the polymer composition and thepolymerization initiator. If the content of the polymerization initiatoris less than 0.05 mass part, the shortage will be at a disadvantage inincreasing the amount of the unaltered monomer component andconsequently increasing the residual monomer content in the producedporous cross-linked polymer. Conversely, if the content of thepolymerization initiator exceeds 25 mass parts, the excess will be at adisadvantage in rendering the polymerization difficult to control anddegrading the mechanical property of the produced porous cross-linkedpolymer.

Alternatively, a redox polymerization initiator formed by combining thepolymerization initiator mentioned above with a reducing agent may beused. In this case, the polymerization initiator to be used herein doesnot need to be discriminated between the water-soluble type and theoil-soluble type. It is permissible to use a water-soluble redoxpolymerization initiator and an oil-soluble redox polymerizationinitiator in combination.

In the reducing agents, as concrete examples of the water-solublereducing agents., sodium hydrogen sulfite, potassium hydrogen sulfite,sodium thiosulfate, potassium thiosulfate, L-ascorbic acid, ferroussalts, formaldehyde sodium sulfoxylate, glucose, dextrose, triethanolamine, and diathanol amine may be cited. As concrete examples of theoil-soluble reducing agent, dimethyl aniline, tin octylate, and cobaltnaphthenate may be cited. These redox polymerization initiator typereducing agents may be used either singly or in the form of a mixture oftwo or more members.

The ratio of the reducing agent contained in the redox polymerizationinitiator mentioned above (mass ratio), i.e. the polymerizationinitiator (oxidizing agent)/reducing agent, is in the approximate rangeof 1/0.01-1/10, preferably 1/0.2-1/5.

The polymerization initiator (inclusive of the redox polymerizationinitiator) is only required to be present at least during the course ofthe polymerization of an HIPE. It may be added to the oil phase and/orthe water phase {circle around (1)} prior to the formation of an HIPE,{circle around (2)} simultaneously with the formation of an HIPE, or{circle around (3)} after the formation of an HIPE. In the case of theredox polymerization initiator, the polymerization initiator (oxidizingagent) and the reducing agent may be added at different times.

(f) Salt

The salt as an arbitrary component for the composition of the HIPEmentioned above may be used when it is necessary for improving thestability of the HIPE.

As concrete examples of the salt of this nature, halogenides, sulfates,nitrates, and other similar water-soluble salts of alkali metals andalkaline earth metals such as calcium chloride, sodium sulfate, sodiumchloride, and magnesium sulfate may be cited. These salts may be usedeither singly or in the form of a combination of two or more members.Such a salt is preferred to be added in the water phase. Among othersalts mentioned above, polyvalent metal salts prove particularlyadvantageous from the viewpoint of the stability of the HIPE during thecourse of polymerization.

The content of the salt mentioned above is proper in the range of 0.1-20mass parts, preferably 0.5-10 mass parts, based on 100 mass parts. Ifthe content of the salt exceeds 20 mass parts, the excess will be at adisadvantage in suffering the waste water squeezed out of the HIPE tocontain the water in an unduly large amount, boosting the cost for thedisposal of the waste water, failing to bring a proportional addition tothe effect, and not doing any good economically. If the content is lessthan 0.1 mass part, the shortage will possibly prevent the effect of theaddition of the salt from being fully manifested.

(g) Other Additive

Varying other additive which are capable of improving the conditions ofproduction, the property of HIPE, and the performance of the porouscross-linked polymer by imparting the performance and the function oftheir own, they may be suitably used herein. For example, a base and/ora buffer may be added for the purpose of adjusting the pH value. Thecontent of the other additive may be selected within such a range thatthe additive used may fully manifest the performance, function, andfurther the economy commensurate with the purpose of addition. As suchadditives, activated carbon, inorganic powder, organic powder, metallicpowder, deodorant, antibacterial agent, antifungi agent, perfume andother highly polymerized compounds may be cited.

(2) Method for Preparation of HIPE

The method for production of the HIPE which can be used in thisinvention does not need to be particularly discriminated. Any of themethods for production of HIPE heretofore known to the art may besuitably used. A typical method for the production of interest will bespecifically described below.

First, a polymerizing monomer, a cross-linking monomer, and a surfactantas essential components and further an oil-soluble polymerizationinitiator (inclusive of an oil-soluble redox polymerization initiator)and other additive as optional components for the formation of an oilphase prepared in respectively specified amounts mentioned above arestirred at a prescribed temperature to produce a homogeneous oil phase.

Meanwhile, water as an essential component and further a water-solublepolymerization initiator (inclusive of a water-soluble redoxpolymerization initiator), salts, and other additive as optionalcomponents for the formation of a water phase prepared in respectivelyspecified amounts are stirred and heated to a prescribed temperature inthe range of 30-95° C. to produce a homogeneous water phase.

Then, the oil phase which is the mixture of the monomer component,surfactant, etc. and the water phase which is the mixture of water,water-soluble salt, etc., both prepared as described above are joined,mixed and stirred efficiently for exertion of proper shearing force andinduction of emulsification at the temperature for the formation of anHIPE (emulsifying temperature) which will be described specificallyhereinbelow to accomplish stable preparation of an HIPE. As a means forstirring and mixing the water phase and the oil phase particularly forthe table preparation of the HIPE, the method which comprises keepingthe oil phase stirred and continuously adding the water phase to thestirred oil phase over a period of several minutes to some tens ofminutes. Alternatively, the HIPE aimed at may be produced by stirringand mixing part of the water phase component and the oil phase componentthereby forming an HIPE resembling yogurt and continuing the stirringand mixing operation while adding the remaining portion of the waterphase component to the yogurt-like HIPE.

(3) Water Phase/oil Phase (W/O) Ratio

The water phase/oil phase (W/O) ratio (mass ratio) of the HIPE which isobtained as described above does not need to be particularly limited butmay be properly selected to suit the purpose for which the porouscross-linked polymer material possessed of open cells is used (such as,for example, water absorbent, oil absorbent, sound insulating material,and filter). It is only required to be not less than 3/1 as specifiedabove and is preferred to fall in the range of 10/1 -250/1, particularly10/1-100/1. If the W/O ratio is less than 3/1, the shortage will bepossibly at a disadvantage in preventing the porous cross-linked polymermaterial from manifesting a fully satisfactory ability to absorb waterand energy, lowering the degree of opening, and causing the surface ofthe produced porous cross-linked polymer material to suffer from undulylow degree of opening and fail to exhibit a fully satisfactorypermeability to liquid. The hole ratio of the porous cross-linkedpolymer material is decided by varying the W/O ratio. Thus, the W/Oratio is preferred to be selected so as to impart to the produced porouscross-linked polymer material a hole ratio conforming to the use and thepurpose. When the product is used as a varying absorbent material suchas disposable diaper or sanitary article, for example, the W/O ratio ispreferred to fall in the approximate range of 10/1-100/1. Incidentally,the HIPE which is obtained by stirring and mixing the water phase andthe oil phase is generally a white highly viscous emulsion.

(4) Apparatus for Production of HIPE

The apparatus for the production of the HIPE mentioned above does notneed to be particularly discriminated. Any of the apparatuses for theproduction of the porous cross-linked polymer material which have beenheretofore known to the art may be used. For example, the stirringdevice (emulsifier) to be used for mixing and stirring the water phaseand the oil phase may be selected from among the stirring devices andthe kneading devices which have been heretofore known to the art. Asconcrete examples of the stirring device, stirring devices using vanesof the propeller type, the paddle type, and the turbine type,homomixers, line mixers, and pin mills may be cited.

(5) Forming Temperature of HIPE

The forming temperature of an HIPE (hereinafter referred to as“emulsifying temperature”) is the temperature at which the water phaseand the oil phase of the temperature mentioned above are mixed. It isgenerally in the range of 60-150° C. From the view point of thestability of the HIPE, it is preferably in the range of 75-110° C., morepreferably in the range of 85-110° C., particularly preferably in therange of 80-95° C., and most preferably in the range of 80-90° C. If theforming temperature of the HIPE is less than 60° C., the shortage willbe possibly at a disadvantage in requiring application of heat for along time, depending on the curing temperature. Conversely, if theforming temperature of the HIPE exceeds 150° C., the excess will bepossibly at a disadvantage in causing the formed HIPE to be deficient instability. It is commendable to form a necessary HIPE by preparatorilyadjusting the temperature of the oil phase and/or the water phase to aprescribed emulsifying temperature and stirring and mixing them tillemulsification. Since the amount of the water phase is large during thepreparation of the HIPE, it may well be considered preferable to havethe temperature of at least the water phase adjusted in advance to theprescribed emulsifying temperature. When a polymerization initiator(inclusive of a redox polymerization initiator) is incorporated inadvance of the preparation of the HIPE, the emulsifying temperature ofthe HIPE is preferred to be fixed at a level capable of avoidingsubstantially inducing thermal decomposition of the polymerizationinitiator (oxidizing agent) and consequently initiating thepolymerization of the HIPE. Thus, the emulsifying temperature ispreferred to be lower than the temperature at which the half life of thepolymerization initiator (oxidizing agent) is 10 hours (10-hour halflife temperature).

[II] Production of Porous Cross-linked Polymer Material

(1) Addition of Polymerization Initiator

(a) Time for addition of Polymerization Initiator

This invention contemplates {circle around (1)} adding a polymerizationinitiator to the water phase and/or the oil phase and mixing them priorto the formation of an HIPE, {circle around (2)} simultaneously addingthe polymerization initiator with the formation of the HIPE, or {circlearound (3)} making this addition subsequently to the formation of theHIPE. Even in the case of the addition of {circle around (3)}, a redoxpolymerization initiator may be used similarly in the case of {circlearound (1)} described above regarding the method for forming the HIPE.

(b) Method for Addition of Polymerization Initiator

It is convenient to add preparatorily the polymerization initiator tothe oil phase when the polymerization initiator or the reducing agent isan oil-soluble type or to the water phase when it is in a water-solubletype. Alternatively, the oil-soluble polymerization initiator (oxidizingagent) or the reducing agent may be added in an emulsified form, forexample, to the water phase.

(c) Form of use of Polymerization Initiator

The polymerization initiator may be used in an undiluted form, in theform of a solution in water or an organic solvent, or in the form of adispersion. When the addition is made either simultaneously with orsubsequently to the formation of the HIPE, it is important that theadded polymerization initiator be quickly and homogeneously mixed withthe HIPE for the purpose of avoiding the otherwise possibleheterogeneous polymerization of the monomer component. Further, the HIPEwhich has been mixed with the polymerization initiator is quicklyintroduced into a polymerization vessel or a continuous polymerizingdevice as means for polymerization. It is commendable from this point ofview to insert a path for the introduction of a polymerization initiatorsuch as a reducing agent or an oxidizing agent in the path extendingfrom the emulsifying device for preparing the HIPE through thepolymerization vessel or the continuous polymerizing device, adding thepolymerization initiator via the path to the HIPE, and mix them by meansof a line mixer.

If the HIPE which contains the polymerization initiator has a smalldifference between the emulsifying temperature and the polymerizingtemperature thereof, the closeness of the emulsifying temperature to thepolymerizing temperature will possibly set the polymerizing monomer orthe cross-linking monomer polymerizing during the course of theemulsification and suffer the resultant polymer to impair the stabilityof the produced HIPE. Thus, the method of adding the reducing agent orthe oxidizing agent or other polymerization initiator to the HIPEimmediately prior to the polymerization, i.e. the method of {circlearound (2)} or {circle around (3)} mentioned above, proves advantageous.

The amount of the polymerization initiator to be used herein equals thatin the method described above under the title of the method forpreparation of HIPE.

(2) Polymerization of HIPE

(a) Method for Polymerization

The method for polymerizing the HIPE mentioned above does not need to beparticularly discriminated. Any of the known methods for polymerizationof an HIPE may be properly adopted to suit the occasion. Generally, thispolymerization is carried out by the method of stationary polymerizationunder conditions incapable of breaking the structure of water dropshighly dispersed in the oil of the HIPE. In this case, the HIPE may bepolymerized batchwise or polymerized continuously while continuouslyfeeding the HIPE in the form of a layer.

For the purpose of utilizing to advantage the effect of short-timepolymerization at an elevated temperature which characterizes thisinvention, the method for polymerization is preferred to be thecontinuous polymerization which can elevate the temperature of the HIPEmore easily than the batch polymerization. It is commendable, forexample, to adopt a method for continuous polymerization which comprisescontinuously forming the HIPE in the form of a layer on a belt in motionand polymerizing the layer of HIPE on the belt. Specifically, as atechnique for continuous polymerization of a porous cross-linked polymerin the form of a sheet, a method which comprises continuously supplyingan HIPE onto a belt in motion which is so constructed as to heat thesurface of a belt of a bent conveyor by a heating device andpolymerizing the HIPE meanwhile shaping the HIPE in the form of a smoothsheet on the belt may be cited. When the surface of the conveyor whichcontacts the emulsion is flat and smooth, the polymer in the form of acontinuous sheet can be obtained in a necessary thickness by supplyingthe HIPE in the necessary thickness onto the belt. Since this inventionis capable of preparing the HIPE at an elevated temperature, the methodof continuous polymerization which continuously polymerizes the HIPEproves advantageous because it enjoys high efficiency of production andutilizes most efficiently the effect of curtailing the polymerizationtime. Further, the procedure of polymerizing the HIPE meanwhileconveying the HIPE horizontally in the form of a sheet as describedabove constitutes itself a preferred mode even in consideration of thefact that the oil phase and the water phase of the HIPE are possessed ofa comparatively friable behavior of easily deflecting and separating inthe vertical direction. Even in this case, the HIPE can be polymerizedin the form of a block or a sheet and then worked in a necessary shapeby cutting the block into sheets each measuring 5 mm in thickness.

(b) Polymerizing Temperature

The polymerizing temperature of the HIPE of this invention does not needto be particularly discriminated. It can be polymerized by the knowntemperature. It is generally in the range of 60-150° C. From theviewpoint of the stability of the HIPE and the speed of polymerization,it is preferably in the range of 75-130° C., and particularly preferablyin the range of 85-110° C. If the polymerizing temperature is lower than60° C., the shortage will be possibly at a disadvantage in necessitatingan unduly long time for polymerization and rendering commercialproduction unfavorable. Conversely, if the polymerizing temperatureexceeds 150° C., the excess will be possibly at a disadvantage incausing the produced porous cross-linked polymer material to suffer fromununiform pore diameters. Optionally, the polymerizing temperature maybe varied in two stages or in more stages during the process ofpolymerization. This invention does not exclude this manner of effectingthe polymerization.

(c) Polymerizing Time

The polymerizing time of an HIPE in the present invention does not needto be particularly discriminated. Generally, it's in the range of oneminute-20 hours. It is preferably within one hour, more preferablywithin 30 minutes, and particularly preferably in the range of one-20minutes. For the purpose of completing the polymerization of the HIPEwithin one hour, it is commendable to fix the amount of thepolymerization initiator to be completely decomposed within thepolymerizing time in the range of 0.05-5.0 mol %, preferably in therange of 1-3 mol %, based on the amount of the monomer component. Whenthe number of radicals to be generated by the decomposition of thepolymerization initiator is n>2, the value of the amount of thepolymerization initiator in the range multiplied by n>2. This valuerepresents the amount of the polymerization initiator to be completelydecomposed within the polymerizing time. The kind and the amount of thepolymerization initiator and the polymerizing temperature to be used areset so that the amount in question falls in the range just mentioned.When these factors are to be set, they may be properly selected inconsideration of the half-time temperature of the relevantpolymerization initiator, for example. If the polymerizing time is lessthan one minute, the shortage will be possibly at a disadvantage inpreventing the porous cross-linked polymer material from acquiringsatisfactory strength. Naturally, this invention does not need topreclude adoption of a longer polymerizing time than the range mentionedabove.

After the polymerization, the formed polymer is cooled, graduallyoptionally, to the prescribed temperature which does not need to beparticularly limited. The porous cross-linked polymer material obtainedby the polymerization, when necessary, may be transferred to the processof such after treatment as the dehydration or the compression which willbe described specifically herein below.

(d) Apparatus for Polymerization

The apparatus for polymerization which can be used in this inventiondoes not need to be particularly discriminated. It may be properlyselected to suit the relevant method of polymerization from the knownchemical devices and put to use, optionally in a modified form. In thebatch polymerization, for example, a polymerization vessel having ashape fit for the purpose of use. In the case of the continuouspolymerization, a belt conveyor type continuous polymerizing devicefurnished with compressing rollers may be used. The apparatus ofinterest may additionally incorporate therein temperature elevatingmeans or controlling mens which fits the relevant method ofpolymerization such as, for example, temperature elevating means capableof quickly elevating the temperature to the curing temperature by theuse of the active thermal energy ray such as microwaves or infrared rayswhich can utilize the radiation energy or the thermal medium such as hotwater or hot air. The apparatus for polymerization that can be used inthis invention does not need to be limited thereto. Further in the caseof batch polymerization, the upper and lower surfaces of the mass of theHIPE introduced into the polymerization vessel are preferred to beprevented from contacting the ambient air, particularly the oxygencontained in the air from the start of polymerization through thecompletion thereof. These surface parts are necessary for the purpose ofinfallibly securing the structure of open cells. Thus, in the case ofthe belt conveyor type continuous polymerization, a PET film is spreadon the belt conveyor engaged in supplying the HIPE and, after the supplyof the HIPE, a sealing material such as a PET film is mounted on theHIPE to seal the HIPE from the ambient air. The material for thepolymerization apparatus does not need to be particularly discriminated.Metals such as aluminum, iron, and stainless steel, synthetic resinssuch as polyethylene, polypropylene, fluorine resin, polyvinyl chloride,and unsaturated polyester resin, and fiber-reinforced resins such as thesynthetic resins mentioned above which are reinforced with such fibersas glass fibers or carbon fibers may be used.

(3) Step of Aftertreatment (Conversion into Finished Product) AfterFormation of Porous Cross-linked Polymer Material

(a) Dehydration

The porous cross-linked polymer material formed in consequence of thecompletion of polymerization is normally dehydrated by compression,aspiration under reduced pressure, or the combination thereof. By thisdehydration, generally 50-98% of the water used is removed and theremainder thereof is left adhering to the porous cross-linked polymermaterial.

The ratio of dehydration is properly set to suit the purpose for whichthe produced porous cross-linked polymer material is used. Generally,the water content in the porous cross-linked polymer material in aperfectly dried state is set at a level in the range of 1-10 g,preferably 1-5 g, per g of the polymer material.

(b) Compression

The porous cross-linked polymer of this invention can be obtained in aform compressed to one of several divisions of the original thickness.The compressed sheet has a smaller inner volume than the original porouscross-linked polymer and permits a decrease in the cost oftransportation or storage. The porous cross-linked polymer in thecompressed state is characterized by being disposed to absorb water whenexposed to a large volume of water and resume the original thickness andexhibiting the ability to absorb water at a higher speed than theoriginal polymer.

From the viewpoint of saving the space for transportation or storage andfacilitating the handling, it is effective to compress the polymer tonot more than ½ of the original thickness. Preferably, the compressionis made to not more than ¼ of the original thickness.

(c) Cleaning

For the purpose of improving the surface condition of the porouscross-linked polymer, the porous cross-linked polymer may be washed withpure water, an aqueous solution containing an arbitrary additive, or asolvent.

(d) Drying

The porous cross-linked polymer obtained by the preceding steps, whennecessary, may be dried by heating as with hot air or microwaves or maybe moistened for adjustment of the water content.

(e) Cutting

The porous cross-linked polymer obtained by the preceding steps, whennecessary, may be cut in expected shape and size and fabricated into afinished product fitting the purpose of use.

(f) Impregnation

The polymer may be endowed with functionality by being impregnated witha detergent or an aromatic agent.

EXAMPLES

Now, this invention will be described more specifically below withreference to working examples and comparative examples. The scope ofthis invention is not limited by these examples. The properties of theporous cross-linked polymer material which are reported in these workingexamples were determined and rated as follows.

Ratio of Free swelling

A sample cut in the cube of 1 cm was dried and weighed and immersed inan ample amount of purified water. The sample swelled by absorbing thepurified water was left standing and draining for 30 seconds on a glassfilter 120 mm in diameter and 5 mm in thickness (made by Duran Corp. andsold under the product code of “#0”). The sample now wet with theabsorbed water was weighed. The ratio of free swelling (g/g) of theporous cross-linked polymer material was calculated in accordance withthe formula 2 shown below using the weight found as above.

Ratio of free swelling (%)=[(Mass of sample after absorbing water−Weightof sample before absorbing water)/(Mass of sample before absorbingwater)]×100  Formula 1:

Flexibility

A sample swelled in physiological saline solution at 37° C. is cut intotest pieces measuring 7×0.8×0.8 cm. A test piece is bent round acylindrical mandrel 0.8 cm in diameter at a uniform speed for fiveseconds. When the test piece is neither torn nor broken throughout theperiod of this test, the porous cross-linked polymer material affordingthis sample is rated as possessing flexibility.

Resistance to Compression Strain

A sample was cut to obtain a disc 5 mm in thickness and 2.87 cm indiameter. The disc was immersed in a physiological saline solution at32° C. The disc in the immersed state was tested for thickness under noload by the use of a dead-load thickness meter (made by Ono SokkiseizoK.K. and sold under the trademark designation of “Digital Linear GaugeModel EG-225”). After the elapse of 15 minutes then, the sample was heldunder a load of 5.1 kPa. When the mass of the sample reached the stateof equilibrium, the thickness of the sample under the load was measured.The resistance to compression strain (RTCD) (%) was calculated inaccordance with the formula 2 shown below.

 R.T.C.D. (%)=[(Thickness under no load−Thickness under load)/(Thicknessunder no load)]×100   Formula2:

Synthesis Example 1 Synthesis of (Meth)acryl Type Cross-linked Polymer(1)

A reaction vessel provided with a thermometer, a condenser tube, a gasinlet tube, and a stirrer was charged with 93 mass parts of methylmethacrylate and 7 mass parts of methacrylic acid and displaced withnitrogen gas. Then, the resultant mixture was stirred and meanwhileheated to 80° C. The stirred and heated mixture and 1 mass part ofazobisisobutyronitile as a polymerization initiator and 4 mass parts ofn-dodecyl mercaptan as a chain transfer agent added thereto weretogether copolymerized for four hours. Then, the polymerization wasstopped by blowing air into the system and, at the same time, adding0.01 mass part of hydroquinone thereto.

Then, the contents of the reaction vessel, after adding 5.8 mass partsof glycidyl methacrylate and 0.1 mass part of triethyl amine as anesterifying catalyst, was heated to 100° C. and left reacting under anatmosphere of air for five hours to synthesize a mixture (1) of a(meth)acryl cross-linked polymer having a solid component concentrationof 51%, a weight average molecular weight of the solid component of17,000 determined by gel permeation chromatography and reduced topolystyrene and a polymerizing monomer (hereinafter referred to as“cross-linking methacryl syrup”). The polymer component and the monomercomponent contained in the produced cross-linking methacryl syrup wereseparated. by reprecipitation. The double bond equivalent contained inthe polymer was found to be 2,300 g/mol.

Synthesis Example 2 Synthesis of (Meth)acryl Cross-linking Polymer (2)

The same reaction vessel as used in Synthesis Example 1 was charged with94.1 mass parts of methyl methacrylate and 5.9 mass parts of glycidylmethacrylate and displaced with nitrogen gas. Then the resultant mixturewas stirred and meanwhile heated to 80° C. The stirred and heatedmixture and 1 mass part of azobisisobutyronitrile and 4 mass parts ofn-dodecyl mercaptan added thereto were together copolymerized for fourhours. The polymerization was stopped by blowing air into the systemand, at the same time, adding 0.01 mass part of hydroquinone thereto.Then, the contents of the reaction vessel, after adding 3.5 mass partsof methacrylic acid and 0.1 mass part of triethyl amine, was heated to100° C. and left reacting under an atmosphere of air for five hours tosynthesize a cross-linking methacryl syrup (2). The physical constantsof the produced cross-linking methacryl syrup (2) are 50% of solidcomponent concentration, 16000 of weight average molecular weight, 35poises of viscosity, and 3500 g/mol of double bond equivalent weight.

Synthesis Example 3 Synthesis of (Meth)acrylic Type Cross-linkingPolymer (2)

A flask having an inner volume of 2000 ml and provided with athermometer, a condenser tube, a gas inlet tube, and a stirrer wascharged with 200 mass parts of ethyl acetate. The contents of the flaskwas heated to the boiling point, with the gas entrapped thereindisplaced with nitrogen gas. To the heated contents of the flask, 20mass % of a polymerizing unsaturated monomer (A) composed of 460 massparts of butyl acrylate, 460 mass parts of 2-ethylhexyl acrylate, and 72mass parts of acrylic acid was introduced. Subsequently, 20 mass % of apolymerization initiator solution composed of 95.2 mass parts ofpentaerythritol tetrakisthio-glycolate, 0.25 mass part of2,2′-azobisisobutyronitrile, and 100 mass parts of ethyl acetate wasintroduced to initiate polymerization. After 30 minutes following thestart of polymerization, the dropwise addition of the polymerizingmonomer mixture and the initializing agent solution was started andcompleted in 2.5 hours. A booster composed of 1.0 mass part of2,2′-azobis-isobutylonitrile and 10 mass parts of, ethyl acetate wasdivided into two equal portions and these portions were introduced 30minutes and 60 minutes after completion of the dropwise addition and theresultant contents were left aging for 90 minutes. The liquid polymersolution which contained a stellate polymer consequently obtained had aninvolatile substance concentration of 77.2 mass %, a polymerizationratio of 98.5%, a number average molecular weight of 3,800 (Mn), aweight average molecular weight of 5,700 (Mw), a molecular weightdistribution (Mw/Mn) of 1.50. Thus, the polymer had a narrowdistribution of molecular weight.

Then, the heating was continued to remove the solvent and expel thevolatile component. After 90 minutes following the start of the removalof the solvent, the inner temperature of the flask reached 131° C. andthe non-volatile component concentration reached 99.8 mass %. With theinner temperature of the flask cooled to 90° C., the contents of theflask and 0.373 mass part of topanol as a polymerization inhibitor, 142mass parts of glycidyl methacrylate, and 2.86 mass parts of benzyltributyl ammonium chloride as a reaction catalyst added thereto wereleft reacting together for 8 hours to obtain a reacting liquid polymer(1) having introduced a methacrylic ester group, i.e. a polymerizingunsaturated group, through the medium of the carboxyl group the theliquid polymer and the epoxy group of the glycidyl methacrylate.

The reacting liquid polymer (1) had a number average molecular weight of4,200 (Mn); a weight average molecular weight of 7,000 (Mw), a molecularweight distribution (Mw/Mn) of 1.65, a double bond equivalent of 1,530g/mol, and viscosity at 23° C. of 17,500 cpm.

EXAMPLE 1

A water phase to be used in a continuous type emulsion process for theformation of a high water content of water in oil type emulsion wasprepared by dissolving 36.3 kg of calcium chloride anhydride and 568 gof potassium persulfate in 378 liters of purified water. An oil phasewas obtained by adding 960 g of decaglyceryl trioleate to a mixture of500 g of styrene, 3800 g of 2-ethylhexyl alcrylate, 2140 g of 55%divinyl benzene, 880 g of 1,6-hexane diol diacrylate, and 680 g of thecross-linking methacryl syrum (1). The water phase was supplied at atemperature of 80° C. at a flow volume of 56.5 cm³/s and the oil phasewas supplied at a temperature of 22° C. at a flow volume of 1.13 g/srespectively to a dynamic mixing device, completely mixed therein with apin impeller rotating at 1800 rpm, with part thereof recycled at a flowvolume of 57.6 cm³/s at 79° C. to obtain an HIPE. The resultant HIPE wascast between sheet materials (PET film) 203, 205 mounted on an apparatusillustrated in FIG. 1, controlled to a thickness of 5 mm, moved on anendless belt type conveyor 201, and passed through a polymerizationfurnace 215 set at an inner temperature of 80° C. at a moving speed of15 cm/min and polymerized therein for 60 minutes to obtain a porouscross-linked polymer material as a cured substance. The porouscross-linked polymer material 102 thus obtained was dehydrated and driedto obtain a porous cross-linked polymer material.

The produced porous cross-linked polymer material had a free swellingratio of 47 g/g and a low RTCD of 9%, showed only small strain underpressure, exhibited satisfactory behavior under pressure, possessedflexibility, and excelled in performance.

EXAMPLE 2

A porous cross-linked polymer material was obtained by following theprocedure of Example 1 while using 680 g of Kayarad GPO-303 (having adouble bond equivalent of 143 g/mol, made by Nippon Kayaku Co., Ltd.) asa cross-linking agent possessed of an alkylene oxide moiety in the placeof 680 g of the cross-linking methacryl syrup (1). The produced porouscross-linked polymer material had a free swelling ratio of 47 g/g and alow RTCD of 6%, showed only small strain under pressure, exhibitedsatisfactory behavior under pressure, possessed of flexibility, andexcelled in performance.

EXAMPLE 3

An HIPE was obtained by following the procedure of Example 1 while usinga water phase of 85° C. in the place of the water phase of 80° C. Theproduced HIPE was cast between the PET films mounted on an apparatus ofFIG. 1, controlled to a thickness of 5 mm, then moved on a ribbon ofplate, passed through a polymerization furnace set at an innertemperature of 95° C at a moving speed of 1.25 m/min, and polymerizedtherein for eight minutes to obtain a cured polymer. The cured polymerwas dehydrated and dried to obtain a porous cross-linked polymermaterial. The porous cross-linked polymer material had a free swellingratio of 47 g/g and a low RTCD of 8%, showed only small strain underpressure, manifested satisfactory performance under pressure, possessedof flexibility, and excelled in performance.

EXAMPLE 4

An HIPE was obtained by following the procedure of Example 1 while using680 g of a cross-linking methacryl syrup (2) in the place of 680 g ofthe cross-linking methacryl syrup (1). The HIPE was cast between PETfilms, controlled to a thickness of 5 mm, moved on a ribbon of plate,and passed through a polymerization furnace set at an inner temperatureof 80° C. at a moving speed of 30 cm/min, and polymerized therein for 30minutes to obtain a cured polymer. The cured polymer thus obtained wasdehydrated and dried to obtain a porous cross-linked polymer material.The porous cross-linked polymer material had a free swelling ratio of 47g/g and a low RTCD of 8%, showed only small strain under pressure,exhibited satisfactory performance under pressure, possessed offlexibility, and excelled in performance.

EXAMPLE 5

A porous cross-linked polymer material was obtained by following theprocedure of Example 1 while using 680 g of Kayarad TPA-330 (having adouble bond equivalent of 157 g/mol, made by Nippon Kayaku Co., Ltd.) inthe place of 680 g of the cross-linking methacryl syrup (1). Theproduced porous cross-linking polymer material had a free swelling ratioof 47 g/g and a low RTCD of 7%, showed only small strain under pressure,exhibited satisfactory performance under pressure, possessed offlexibility, and excelled in performance.

EXAMPLE 6

An HIPE was obtained by following the procedure of Example 1. In aplastic vessel having an inner volume of 600 cc, 250 g of the HIPE wasplaced, sealed with a stopper, and polymerized by being immersed in awater bath set at 65° C. for 16 hours to obtain a cured polymer. Thecured polymer was sliced into pieces 5 mm in thickness, dehydrated, anddried to obtain a porous cross-linked polymer material. The porouscross-linked polymer material thus obtained had a free swelling ratio of47 g/g and a low RTCD of 9%, showed only small strain under pressure,exhibited satisfactory performance under pressure, possessed offlexibility, and excelled in performance.

EXAMPLE 7

An HIPE was obtained by following the procedure of Example 2. In aplastic vessel having an inner volume of 600 cc, 250 g of the HIPE wasplaced, sealed with a stopper, and polymerized by being immersed in awater bath set at 80° C. for 60 minutes to obtain a cured polymer. Thecured polymer was sliced into pieces 5 mm in thickness, dehydrated, anddried to obtain a porous cross-linked polymer material. The porouscross-linked polymer material thus obtained had a free swelling ratio of47 g/g and a low RTCD of 6%, showed only small strain under pressure,exhibited satisfactory performance under pressure, possessed offlexibility, and excelled in performance.

Comparative Example 1

A porous cross-linked polymer material was obtained by following theprocedure of Example 1 while using an oil phase obtained by adding 960 gof decaglyceryl trioleate to a mixture of 500 g of styrene, 4400 g of2-ethylhexyl acrylate, 2410 g of 55% divinyl benzene, and 960 g of1,6-hexane diol diacrylate. The produced porous cross-linked polymermaterial had a free swelling ratio of 47 g/g and a high RTCD of 12%,showed large strain under pressure, and exhibited poor performance underpressure.

Comparative Example 2

An HIPE was obtained by following the procedure of Example 1 while usingan oil phase obtained by adding 960 g of decaglyceryl trioleate to amixture of 500 g of styrene, 4400 g of 2-ethylhexyl acrylate, 2140 g of55% divinyl benzene, and 960 g of 1,6-hexane diol diacrylate. In aplastic vessel having an inner volume of 600 cc, 250 g of the HIPE wasplaced, sealed with a stopper, and then polymerized by being immersed inwater bath set at 65° C. for 16 hours to obtain a cured polymer. Thecured polymer was sliced into pieces 5 mm in thickness and thendehydrated and dried to obtain a porous cross-linked polymer material.The porous cross-linked polymer had a free swelling ratio of 47 g/g butpossessed no flexibility and exhibited poor performance.

Comparative Example 3

An HIPE was obtained by following the procedure of Example 1 while usingan oil phase obtained by adding 960 g of decaglyceryl trioleate to amixture of 500 g of styrene, 4400 g of 2-ethylhexyl acrylate, 2140 g of55% divinyl benzene, and 960 g of 1,6-hexane diol diacrylate. In aplastic vessel having an inner volume of 600 cc, 250 g of the HIPE wasplaced, sealed with a stopper, and then polymerized by being immersed inwater bath set at 80° C. for 60 minutes to obtain a cured polymer. Thecured polymer was sliced into pieces 5 mm in thickness and thendehydrated and dried to obtain a porous cross-linked polymer material.The porous cross-linked polymer had a free swelling ratio of 47 g/g anda high RTCD of 12% and manifested large strain under pressure andexhibited poor performance under pressure.

EXAMPLE 8

A porous cross-linked polymer material was obtained by repeating theprocedure of Example 6 while forming an oil phase by adding 448 g ofdiglycerine monooleate and 72 g of ditallow dimethyl ammonium chlorideto a mixture of 3288 g of 2-ethylhexyl acrylate, 2640 g of 42% divinylbenzene, 960 g of 1,6-hexane diol diacrylate, and 1112 g of the reactingliquid polymer (1) obtained in Synthesis Example 3, supplying a waterphase at a temperature of 65° C. into a dynamic mixing device, mixingthe oil phase and the water phase, and emulsifying them.

When the porous cross-linked polymer material was rated in the samemanner as in Example 1, it was found to have a free swelling ratio of 47g/g and a low RTCD of 7%, show small strain under pressure, manifestsatisfactory performance under pressure, possess of flexibility, andexcel in performance.

EXAMPLE 9

A porous cross-linked polymer material was obtained by repeating theprocedure of Example 1 while forming an oil phase by adding 448 g ofdiglycerine monooleate and 72 g of ditallow dimethyl ammonium chlorideto a mixture of 3856 g of 2-ethylhexyl acrylate, 2640 g of 42% divinylbenzene, 960 g of 1,6-hexane diol diacrylate, and 544 g of the reactingliquid polymer (1) obtained in Synthesis Example 3.

When the porous cross-linked polymer material was rated in the samemanner as in Example 1, it was found to have a free swelling ratio of 47g/g and a low RTCD of 8%, show small strain under pressure, manifestsatisfactory performance under pressure, possess of flexibility, andexcel in performance.

Industrial Applicability

According to this invention, a porous cross-linked polymer materialexcelling in absorbancy and flexibility can be produced by incorporatingin the monomer mixture a compound having a double bond equivalent of notless than 120 g/mol. Moreover, by using the compound having a doublebond equivalent of not less than 120 g/mol, it is made possible toadjust the cross-link density and advance the occurrence of the gelpoint and eventually curtail the polymerizing time.

What is claimed is:
 1. A method for the production of a porouscross-linked polymer material, the method comprising polymerizing awater-in-oil type high internal phase emulsion containing across-linking agent, characterized by at least one kind of saidcross-linking agent being a compound having a double bond equivalent ofnot less than 120 g/mol.
 2. The method of claim 1, wherein saidcross-linking agent is a compound having an alkylene oxide moiety. 3.The method of claim 2, wherein said compound is a compound having anunsaturated carboxylic acid monomer bonded by ester linkage to analkylene oxide adduct of a polyhydric alcohol.
 4. The method of claim 2,wherein said compound is a compound represented by the following formula(I)

wherein the plurality of R's may be the same or different and are eachhydrogen atom or a methyl group and a, b, and c are each 0 or an integerand satisfy a+b+c≧1 or

wherein the plurality of R's may be the same or different and are each ahydrogen atom or a methyl group, R′ represents a methyl group or anethyl group, m, a, and b are each 0 or an integer, and satisfy m≧1 anda+b=3.
 5. The method of claim 1, where said compound is a vinyl polymercontaining not less than two polymerizing double bonds in the molecularunit.
 6. The method of claim 5, wherein said vinyl polymer is a(meth)acryl cross-linked polymer.